The present disclosure relates generally to antennas for portable, handheld communication devices, and more particularly to designing an antenna for operation at specific radio frequencies.
Different types of wireless mobile communication devices, such as personal digital assistants, cellular telephones, and wireless two-way email communication equipment, cellular smart-phones, wirelessly enabled notebook computers, are available. Many of these devices are intended to be easily carried on the person of a user, often compact enough to fit in a shirt or coat pocket.
As the use of wireless communication equipment continues to increase dramatically, a need exists for increased system capacity. One technique for improving the capacity is to provide uncorrelated propagation paths using Multiple Input, Multiple Output (MIMO) systems. A MIMO system employs a number of separate independent signal paths, for example by means of several transmitting and receiving antennas.
MIMO systems, employing multiple antennas at both the transmitter and receiver offer increased capacity and enhanced performance for communication systems without the need for increased transmission power or bandwidth. The limited space in the enclosure of the mobile communication device, however presents several challenges when designing such multiple antennas assemblies. An antenna should be compact to occupy minimal space and its location is critical to minimize performance degradation due to electromagnetic interference. Bandwidth is another consideration that the antenna designers face in multiple antenna systems.
The size of the antenna is dictated by the radio frequency or band of frequencies at which the antenna is intended to resonate and operate Typically, the physical length of the antenna is a fraction of the wavelength of the operating frequency, for example one-fourth or one-half the wavelength of the radio frequency signal, thus enabling the antenna to resonate at the respective operating frequency. The required physical size for the antenna, to resonate at a certain frequency, is known as the resonant length. For example, an antenna which requires a length equal to quarter of the wavelength of the resonance frequency is known to have a resonant length of a quarter of a wavelength. This size requirement limits how small the antenna can be constructed and thus the amount of space in the housing of the mobile communication device that is occupied by the antenna.
Nevertheless, it is desirable to further reduce the size of the antenna so it can be fit in the small space designated for the antenna in the communication device, especially when the communication device has multiple antennas.